#include <stdio.h>
#include <math.h>

int main() {
    double x1, y1, x2, y2;

    // 读取输入
    printf("请输入两个点的坐标（格式：x1 y1 x2 y2）：");
    scanf("%lf %lf %lf %lf", &x1, &y1, &x2, &y2);

    // 计算两点之间的距离
    double distance = sqrt((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2));

    // 输出结果，保留两位小数
    printf("%.2f\n", distance);

    return 0;
}
